Generally, filmmakers undergo the tortuous, years-long process of making a feature film for two reasons: They have something to say, and their financiers want to make money while they say it. Some movies, however, enter production owing to more unusual motivations. Take a look at five films that originated out of unique circumstances.

1. Raging Bull Got a Green Light from Rocky Balboa

In 2013’s Grudge Match, Sylvester Stallone and Robert De Niro cashed in the equity of their iconic roles as boxers to portray aging rivals getting in the ring for one last bout. But if not for the success of Stallone’s Rocky, De Niro may have never gotten his passion project, 1980’s Raging Bull, made.

De Niro met boxer Jake LaMotta after reading the embattled fighter’s autobiography and became obsessed with telling his story. He convinced director Martin Scorsese to join him; Scorsese had just finished a film, New York, New York with producer Irwin Winkler. Winkler had helped usher Rocky to screens in 1976 and had a deal with United Artists. Despite the talent assembled, UA wasn’t keen on a melancholic tale of an abusive pugilist. But Winkler had ammunition: He knew the studio was desperate for a Rocky sequel. In a slick move, Winkler told them the only way they’d be getting Stallone back in the ring would be to finance Winkler’s other, far less marketable boxing film.

“So we said to them, ‘Well, you want to make Rocky II?’” Winkler told National Public Radio in 2007. “'We'll make Rocky II, but you have to make Raging Bull.’ [B]ut the sad thing is that Raging Bull might never had been made and probably wouldn't have been made unless we took that position on Rocky.”

The studio bit: Rocky II made over $200 million in worldwide box office in 1979. Raging Bull followed in 1980. Though not nearly as profitable as Stallone’s crowd-pleaser, it earned De Niro a Best Actor Oscar and a regular spot on lists covering the best American films ever made.

2. A High School Class Convinced Francis Coppola to Make The Outsiders

S.E. Hinton’s novel of juvenile class struggle, The Outsiders, is said to have practically invented the young adult market. Circulating in classrooms since its release in 1967, the book has sold more than 10 million copies. But it was one school in particular that helped it achieve a first-rate feature adaptation.

In 1980, Jo Ellen Misakian, the librarian of a small Fresno, California grade and middle school, wrote a letter to director Francis Ford Coppola imploring him to consider making a film based on Hinton’s work. More than 100 students signed her petition; she included a copy, presumably to spare Coppola a trip to the bookstore.

“I feel our students are representative of the youth of America,” Misakian wrote. “Everyone who has read the book, regardless of ethnic or economical background, has enthusiastically endorsed this project.”

Coppola’s production company reviewed both the petition and the book: Producer Fred Roos flew out to Tulsa, Oklahoma to meet with Hinton. Coppola wound up optioning the novel, though Roos—in continued correspondence with the school—cautioned there might be rights issues with the title and even asked students to come up with alternatives.

The Outsiders shot in 1982 for a 1983 release: Coppola directed one of the most substantial casts in film history (Patrick Swayze, Tom Cruise, Rob Lowe, Matt Dillon, and Diane Lane). As a thank you, Warner Bros. sent a print of the movie and several of the actors, including Swayze and Ralph Macchio, to the school for a special screening, where students declared it “rad.”

3. Bill Murray Ghost-Busted On One Condition

Thanks to his stint on Saturday Night Live and hit movies like Stripes, Hollywood wanted to be in the Bill Murray business. One script virtually tailor-made for the actor was 1984’s Ghostbusters, co-written by SNL co-star Dan Aykroyd and actor Harold Ramis. But being an ensemble piece meant it was hard to attract name talent to the project; Eddie Murphy was among those who passed.

At the time Ghostbusters was being shopped, Murray had decided to try his hand at dramatic performing and became infatuated with filming an adaptation of W. Somerset Maugham’s The Razor’s Edge. Leveraging his comedic celebrity, Murray told Columbia Pictures he’d agree to star in their big-budget comedy if they financed his pet project about a war veteran on a spiritual quest. They agreed, and while The Razor’s Edge failed to find an audience, Ghostbusters became one of the most popular comedies of all time. (These days, no amount of bartering seems able to convince Murray to do a second Ghostbusters sequel; he’s avoided the project for years.)

4. The Movie Inspired By a Classified Ad

In 1997, Backwoods Home Magazine published a bizarre classified notice. “Wanted: Somebody to go back in time with me,” it read. “This is not a joke … Safety not guaranteed. I have only done this once before.”

The ad was so peculiar that it eventually found a home as a meme, with people circulating it online and speculating as to its authorship. Screenwriter Derek Connolly thought it might make an interesting basis for a film and recommended it to his writing partner, director Colin Trevorrow, as a clever way of heeding their agent’s advice to pitch a film based on a pre-existing concept. The result, 2012’s Safety Not Guaranteed—about a reporter who answers the ad and finds a man who may or may not be preparing to time-travel—garnered positive reviews and developed a cult following.

As for the actual ad? It was written by Backwoods staffer John Silveira because the magazine was running short that issue. Silveira says he received more than 1000 responses, some of which took his offer very seriously. “Dozens, in prison, asked me to go back in time and talk them out of committing the crime that put them away,” he wrote in 2010. “Others … were from people who begged me to go back and save a loved one from a tragic death. Those letters were so heartbreaking I almost couldn't read them and I felt a certain amount of shame for not anticipating the false hope I placed in so many hearts.”

5. The Lambada Movie Made Out of Spite

Producers Menahem Golan and Yoram Globus were two Israeli cousins who made an unlikely impression in Hollywood during the 1980s via their Cannon production banner. Movies involving Chuck Norris, Charles Bronson, and Dolph Lundgren helped populate video store shelves for much of the decade.

But the two eventually had a falling out; by 1990, they no longer shared office space. Globus, who remained with Cannon, decided to pursue an idea they had to do a film based on the then-popular lambada Brazilian dance craze. He teamed with Warner Bros. for the aptly-titled Lambada.

But Golan was not about to let his former business partner hoard the vast profits of fad-based dance films. After Globus had put Lambada in production, Golan announced The Forbidden Dance, a film written in just 10 days and distributed by Columbia. The former partners then circled one another, announcing one release date after the other in the hopes of arriving in theaters first.

Fittingly—or tragically, if one happened to be a moviegoer in spring 1990—their efforts wound up premiering on the very same day. Lambada won the box office duel with $4.8 million compared to Golan’s $1.8 million haul in fewer theaters. The two would later attend a 2010 retrospective of their filmography, their dance-movie rivalry presumably forgotten, before Golan’s passing in 2014.